Electrostatic Potential and CapacitanceNEET MCQs with solutions
Electrostatic Potential and Capacitance covers electric potential, potential difference, equipotential surfaces, capacitors (parallel plate, series/parallel combinations), dielectrics and energy stored in capacitors. NEET tests capacitor numericals, potential calculations and dielectric effects heavily.
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- 12 Physics
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Practise 24 questions
Tap an option to check it. Questions from every NCERT topic in this chapter, from easy to hard.
Q1Mixed Revision
A uniformly charged ring of radius R carries total charge Q. The electric potential at a point on its axis at distance x from the centre is:
Not quite — the answer is D.
Every element of the ring is at the same distance √(x²+R²) from the axial point. Since potential is scalar, all contributions add directly: V=kQ/√(x²+R²). Option C is the trap — students use x²+R² without the square root, confusing the potential formula with the field-magnitude denominator.
Q2Grand Test
Two charges +q and −q are separated by a distance 2a. At a point on the perpendicular bisector of the line joining them, the electric potential due to the dipole is:
Not quite — the answer is A.
Both charges are equidistant from every point on the perpendicular bisector, giving potentials +kq/r and −kq/r that cancel to zero. The trap is confusing potential (scalar, cancels) with the electric field at the same point, which is non-zero and directed antiparallel to the dipole moment.
Q3Electrostatic Potential due to a Point Charge
The electric potential at a distance of 0.2 m from a point charge of +4 μC in air is: (Take k = 9×10⁹ N m² C⁻²)
Not quite — the answer is C.
V = kQ/r = (9×10⁹ × 4×10⁻⁶)/0.2 = 1.8×10⁵ V. Option D (3.6×10⁵ V) is the most common trap — students compute kQ correctly but forget to divide by r = 0.2, effectively using r = 1 m.
Q4Potential due to an Electric Dipole
A short electric dipole of moment p is placed in free space. Using the general dipole potential formula, the electric potential at an axial point (θ = 0°) at distance r is:
Not quite — the answer is B.
V = kp cosθ/r². At axial point θ = 0°, cos0° = 1, so V = kp/r². Option A (2kp/r²) is the axial electric field formula kp/r³ scaled incorrectly — the factor 2 applies to E_axial, not V. NCERT uses the single general formula throughout.
Q5Electrostatic Potential Energy
A charge of +5 μC is placed at a point where the electric potential is 400 V. The potential energy of the charge is:
Not quite — the answer is B.
U = qV = (5×10⁻⁶)(400) = 2.0×10⁻³ J. Option C (4.0×10⁻³ J) is the trap — it results from doubling the charge (using 10 μC instead of 5 μC). Option A results from halving the potential (using 200 V).
Q6Combination of Capacitors
Two capacitors of capacitances 3 μF and 6 μF are connected in series. Their equivalent capacitance is:
Not quite — the answer is A.
1/C_eq = 1/3 + 1/6 = 3/6, so C_eq = 2 μF. Option C (4 μF) traps students who average the two values instead of using the reciprocal formula.
Q7Dielectrics and Polarisation
A dielectric material is best defined as a material that:
Not quite — the answer is B.
Dielectrics are insulators with no free charges. An external field causes bound charges in molecules to shift, forming dipoles. This polarisation reduces the net internal electric field.
Q8Capacitance and Capacitors
Capacitance of a conductor is defined as:
Not quite — the answer is A.
C = Q/V: charge required to raise a conductor's potential by 1 volt. Option C (V/Q) inverts the ratio — the most common definitional error. Capacitance is a geometric property, not dependent on Q or V individually.
Q9Van de Graaff Generator
The primary purpose of a Van de Graaff generator is to produce:
Not quite — the answer is A.
A Van de Graaff generator accumulates charge on a hollow conducting dome to produce very high DC electrostatic potentials of the order of millions of volts. It is not an AC device and produces only a negligibly small current despite the very high voltage.
Q10Potential Energy of a System of Charges
Two point charges +2 μC and +3 μC are separated by 0.30 m in air. The electrostatic potential energy of the system is:
Not quite — the answer is B.
U = kq₁q₂/r = (9e9)(2e-6)(3e-6)/0.30 = 0.18 J. Both charges positive so PE is positive. Option A uses r = 0.60 m by error; Option C doubles the numerator.
Q11Parallel Plate Capacitor
A parallel-plate capacitor of capacitance C is charged to potential V. The battery is then disconnected and the plate separation is doubled. The new capacitance is:
Not quite — the answer is C.
C=ε₀A/d. Doubling d gives C'=ε₀A/(2d)=C/2. Battery disconnection keeps Q constant but does not affect geometric capacitance. Option D (C/4) is the trap for students who wrongly apply a squared relationship.
Q12Conductors in Electrostatic Equilibrium
A conductor is placed in an external electric field and left undisturbed. Which correctly describes the final electrostatic equilibrium state inside the conductor?
Not quite — the answer is A.
Free electrons redistribute to create an induced field that exactly cancels the external field inside. The net E inside becomes zero — this is the definition of electrostatic equilibrium. Options B and D are wrong because any non-zero E inside would continue to drive charge motion.
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Get RankUp on Google PlayQ13Electrostatics of Conductors
The surface of a conductor in electrostatic equilibrium is an equipotential surface. What is the work done in moving a test charge q₀ along the surface of the conductor from point P to point Q?
Not quite — the answer is D.
On an equipotential surface, V is the same at every point, so ΔV = 0. Work done W = q₀ΔV = 0. Option A incorrectly applies W = qEd as if the field drives motion along the surface — but the field is normal to the surface, doing zero work for tangential displacement.
Q14Potential Difference and Work Done
A charge q is moved slowly from point A at potential V_A to point B at potential V_B. The work done by the external agent is:
Not quite — the answer is C.
For slow (quasi-static) displacement, KE does not change, so W_ext = ΔU = q(V_B − V_A). Option A is W_field, not W_ext — the most common sign-reversal error students make when confusing the two work expressions.
Q15Potential due to a System of Charges & Superposition
Three point charges +2q, −q and +q are placed at distances r, r and 2r respectively from point P. What is the electric potential at P?
Not quite — the answer is D.
V = k(2q)/r + k(−q)/r + k(q)/(2r) = 2kq/r − kq/r + kq/(2r) = kq/r + kq/(2r) = 2kq/(2r) + kq/(2r) = 3kq/(2r). Trap: Option A (kq/r) omits the third charge contribution. Potential is scalar — add algebraically with correct signs.
Q16Equipotential Surfaces
An equipotential surface is defined as a surface on which:
Not quite — the answer is B.
Electric potential has the same value at every point — this is the defining property. Electric field is not zero; it is perpendicular to the surface. Option D is wrong because W = qV is identical for all points on the same surface since V is constant.
Q17Effect of Dielectric
A parallel-plate capacitor has capacitance C₀ in air. When completely filled with a dielectric of dielectric constant K, its capacitance becomes:
Not quite — the answer is B.
C'=Kε₀A/d=KC₀. The dielectric replaces ε₀ with Kε₀, increasing capacitance K times. Option D (K²C₀) is the trap for students who square the dielectric constant, confusing it with the energy or charge relationship.
Q18Energy Stored in a Capacitor
A 12 pF capacitor is connected to a 50 V battery. The electrostatic energy stored in the capacitor is:
Not quite — the answer is A.
U=½CV²=½×12×10⁻¹²×2500=15×10⁻⁹ J=15 nJ. Option B (7.5 nJ) results from halving again after the ½ factor, a double-error. Option D arises from omitting the ½ factor entirely and multiplying wrong powers.
Q19Introduction to Electrostatic Potential
The electric potential at a point in an electrostatic field is defined as the work done by an external agent in bringing a unit positive test charge from infinity to that point without changing its kinetic energy. Which statement is correct?
Not quite — the answer is B.
V = W/q; both W and q are scalars, so V is scalar with SI unit J/C (volt). Option A is wrong because scalars have no direction. Option C confuses the unit of electric field (N/C) with that of potential (V = J/C).
Q20Relation Between Electric Field and Potential
The electric field at a point is related to electric potential by which of the following expressions?
Not quite — the answer is B.
Electric field is the negative potential gradient: E = −dV/dr. The negative sign means E points toward decreasing potential (high V to low V). Option A without the negative sign is the most common NEET trap in this topic.
Q21Potential Energy of an Electric Dipole
An electric dipole of moment p is placed in a uniform electric field E with its dipole moment parallel to the field. The force on the dipole and its potential energy are respectively:
Not quite — the answer is D.
In a uniform field, forces on +q and −q are equal and opposite, giving zero net force for any orientation. At θ=0°, U = −pEcos0° = −pE, which is the minimum (most negative) value. Option B is wrong — qE is not zero, and "minimum" alone fails because the force is also not qE.
Q22Introduction to Electrostatic Potential
A conducting sphere of radius R is given a charge Q. The electric potential and electric field at the centre of the sphere respectively are:
Not quite — the answer is A.
Inside a conductor in electrostatic equilibrium, E = 0 everywhere inside, including the centre. Potential is constant throughout and equals the surface value Q/(4πε₀R). Option C is the most common trap: students apply the surface field formula inside the conductor.
Q23Introduction to Electrostatic Potential
The SI unit of electric potential is the volt. Which of the following is an equivalent expression for one volt?
Not quite — the answer is B.
V = W/q gives 1 V = 1 J/C. Option C (N·m) is the unit of work (joule) not potential. Option D (C/J) is the reciprocal. Option A has incorrect dimensions entirely.
Q24Introduction to Electrostatic Potential
Which of the following statements about electric potential is INCORRECT?
Not quite — the answer is D.
With V = 0 at infinity, a negative point charge produces negative potential at all finite distances. So potential is not necessarily positive. Options A, B, and C are all correct NCERT-consistent statements.
ELITE question · AIR under 50 level
This chapter has 228 ELITE questions for students aiming at the very top. They are only in the app.
Unlock ELITE questions in the appKey Potential & Capacitance
Quick revision: most questions in this chapter test these facts.
| Concept | Key Formula |
|---|---|
| Electric potential | V = kQ/r; work done W = qΔV; V is scalar (add algebraically) |
| Parallel plate capacitor | C = ε₀A/d; with dielectric: C = Kε₀A/d |
| Series combination | 1/C_eq = 1/C₁ + 1/C₂; charge same on each; voltage divides |
| Parallel combination | C_eq = C₁ + C₂; voltage same; charge divides |
| Energy stored | U = ½CV² = ½QV = Q²/2C |
| Equipotential surface | Perpendicular to E; no work done moving charge on it |
What the app covers in this chapter
691 questions in total, each with a detailed explanation.
| Mixed Revision | 77 |
| Grand Test | 55 |
| Electrostatic Potential due to a Point Charge | 40 |
| Potential due to an Electric Dipole | 40 |
| Electrostatic Potential Energy | 40 |
| Combination of Capacitors | 40 |
| Dielectrics and Polarisation | 39 |
| Capacitance and Capacitors | 39 |
| Van de Graaff Generator | 39 |
| Potential Energy of a System of Charges | 37 |
| Parallel Plate Capacitor | 36 |
| Conductors in Electrostatic Equilibrium | 28 |
| Electrostatics of Conductors | 26 |
| Potential Difference and Work Done | 20 |
| Potential due to a System of Charges & Superposition | 20 |
| Equipotential Surfaces | 20 |
| Effect of Dielectric | 20 |
| Energy Stored in a Capacitor | 20 |
| Introduction to Electrostatic Potential | 19 |
| Relation Between Electric Field and Potential | 19 |
| Potential Energy of an Electric Dipole | 17 |
Questions students ask
Is Electrostatic Potential and Capacitance important for NEET?
Yes — capacitor combinations, dielectric effects and energy stored in capacitors are tested every year. Numerical problems dominate.
Which topics should I revise first?
Focus on parallel plate capacitor formula, series vs parallel combinations, effect of dielectric on C/V/E/U, energy stored formulas, and potential due to point charges and dipoles.
How many questions from this chapter are on RankUp?
The RankUp app has 691 questions on Electrostatic Potential and Capacitance, including 228 ELITE questions. Every question has a detailed explanation.
